#include <iostream>
using namespace std;

long long countWays(int n) {
    long long a = 1, b = 1;
    while (n-- > 1) {
        long long temp = b;
        b = a + b;
        a = temp;
    }
    return b;
}

int main() {
    int n;
    cin >> n;
    long long result = countWays(n);
    cout << result << endl;
    return 0;
}
